Sensor and method for indicating the presence of a low magnetic field using high critical temperature superconductor ceramic material to absorb electromagnetic energy

A sensor for use with a source of electromagnetic energy for indicating the presence of a low magnetic field with a sensitivity of at least 10.sup.-10 tesla, the sensor comprising:

• a sensing element consisting essentially of a high critical temperature superconductor ceramic oxide material without the need for further processing, said critical temperature being above 77.degree. Kelvin;
• means for cooling the sensing element to a temperature below the critical temperature of the superconductor material whereby the sensing element becomes superconducting;
• means for applying electromagnetic energy from the source to the sensing element whereby a first portion of the applied energy is absorbed by the sensing element;
• means for detecting the amount of the energy absorbed by the sensing element;
• and
• means modulating the sensing element for providing a reference signal for phase-sensitive detection and for biasing the electromagnetic energy absorption characteristics of the sensing element to a predetermined absorption reference value whereby a magnetic field of about 10.sup.-10 tesla or less near the sensing element results in a change in the absorption of the electromagnetic energy by the sensing element, the change being detected by the detecting means to indicate the presence of the magnetic field.